The technology involved in the production of crude petroleum and natural gas encompasses a broad range of techniques and procedures. Important among these are the non-pumping approach or "gas lifting" techniques of production wherein, generally, the wells are operated on an intermittent basis by the utilization of some form of cyclical treatment. With this arrangement, natural gas pressures, whether artificially or naturally induced, are selectively permitted to build at the well bottom until conditions therewithin are such that liquid accumulated within the well, which usually will include oil and salt water, will be expelled by the pressure of the natural gas into separation and collection facilities.
Concerning wells intended principally for natural gas production, rarely occurring is the "dry" natural gas well wherein substantially no liquid hydrocarbons or water are encountered in the course of production. Commonly, such liquids will accumulate in the well to an extent wherein the energy extant in and available from the natural gas production reservoir of the pertinent geologic region is inadequate to permit continuing gas flow. Without correction, the static pressure associated with such fluids eventually may cause a well failure typically termed "loading up." To avoid excessive amounts of this liquid buildup, in the past, a procedure then termed "intermitting" was carried out wherein mechanical clock controllers operating in a limited but repeating time cycle, periodically vented a well to the atmosphere to effect an expulsion of the liquid. Venting to the atmosphere now is considered to be an economically unacceptable procedure. However, the term "intermitting" has been applied to a gas well production procedure wherein the well is produced on a cyclical basis. In this regard, in many geologic areas, for example, in the Appalachian region as well as regions in the Fort Worth basin, gas well production must be cycled in a highly accurate manner. This cyclical treatment involves a "shutting-in" procedure wherein the well is closed for a carefully determined interval of time adequate to allow well pressure to build up sufficiently to expell all fluids upons subsequent opening up. Production only occurs during that relatively short interval wherein fluid and gas are expelled into a sales line system. Then the well again is "shut in" to achieve necessary pressure buildup. As is apparent, the timing of these operations is critical. For example, a typical well may produce for a twenty minute interval following which it must be "shut in" for an interval of four hours. Because the duty cycle of the well is so short, deriving an optimum formula for producing it becomes a taxing endeavor. Many production parameters are considered, no two wells exhibiting the same performance signature, and the performance signature of any given well changing with the age thereof. In many applications, a failure to shut in a well within mere minutes of the proper time envelope of production may result in a complete "loading up" of the well. This represents a failure which may be quite expensive to correct.
Many wells within the noted geologic regions and others serve to produce both natural gas and liquid petroleum in the course of their cyclically controlled operation. Very often to improve their production capabilities, the tubing strings in such wells incorporate a plunger lift device. With this arrangement, when the well is "shut in," the plunger is situate in the lowermost portion of the tubing string. As natural gas pressure develops within the well during the "shut in" interval, a "slug" of liquid accumulates in the tubing string above the plunger. At an optimum point in time, a motor valve coupled between the tubing string and separation and collection equipment is opened to permit the plunger to be propelled to the surface at the wellhead, and fluid and gas which has collected within the string is delivered to appropriate receiving facilites. For example, through the use of separation stages, the liquid petroleum is segregated from the gas and salt water; and the gas cap, for the production interval, is recovered.
For a considerable period of time and including the present day, control over the cyclical production of wells has been one based simply upon a crude hand wound clock-operated device, the cyclical closing and opening of a motor valve being determined by the operator following the periodic monitoring of a variety of parameters such as differential pressure between casing and tubing string, sales line pressure, experience with adjacent wells and the like. With such monitoring, the signature of the well, i.e. the periodic development of pressure differentials optimum for producing and shutting in have been determined and the clock controls were adjusted accordingly. Such periodic operation of the wells was found to be inadequate for a variety of conditions including the difficulties associated with finding reliable operational personnel to periodically visit the wellhead sites and adjust the controlling devices properly. Where such operational maintenance failed, a loading-up condition often was encountered requiring expensive swabbing procedures and the like to clear the tubing.
More recently, a gas well controller system operating upon an electronic basis has been introduced with considerable success to the industry. Described in U.S. Pat. No. 4,150,721 by W. L. Norwood, the electronic controller provided for long-term, battery-operated control over wells and which simplified the control adjustment procedure as required of operators. Of particular importance, the controller responds to system parameters to override the cycle timing provided thereby, conditions often being encountered where the cyclical timing system should be overridden and subsequently reinitiated on an automatic basis. For example, should the tubing pressure at the wellhead fall to a certain predetermined level, an indication may be present that gas is not finding its way through the tubing string and that liquid is building up. Accordingly, such a situation may present an overriding condition calling for shutting in the well. Other conditions may relate to the safe operation of a gas production system. For example, excessive liquid levels in separating systems will call upon an overriding of well cycling as will line pressure fluctuation which can have a particularly deleterious affect upon the production of a well.
Considering wells which function principally to produce liquid petroleum products, an often encountered non-pumping form of production technique involves what is termed as "injection gas lift." With this technique, natural gas from a well or source other than the well being produced is pumped under compression to the lower regions of the well, again on an intermittent basis. The comingling of gas with fluid within the well, for many applications, considerably enhances production output. As before, however, the introduction of such compressed gas into the well should be carried out on a highly accurate basis, such accuracy preferably being to the extent of numbers of seconds. Conventional controllers otherwise used to drive motor valves and the like, may be utilized for the purpose of controlling gas injection systems, however, to the present, the accuracy of control desired has not been met nor has the development of control systems which accommodate to a variety of environmental factors been evolved.
A broad variety of gas and oil well production difficulties have been found to persist in the industry even following the advances achieved with the noted electronic controller system. The inventor named herein has isolated numerous of the operational difficulties which occur notwithstanding the introduction of controller devices which are capable of responding to externally switched phenomena, for example, associated with separator liquid levels, sales line pressures, differential pressures at wellheads, collector tank levels, and the like. Due to the great variety of operational situations which can occur and are heueristically accommodated, a need has developed for a controller system and technique which remains practical in terms of cost while having the flexibility of accommodating a large range of required operational sequences, values, or parameters, each of which may vary in the course of a production cycle.
Another aspect of the controller requirements for fluid hydrocarbon production looks to both the human engineering requirements in view of the level of confidence and competence one may repose in typical operator personnel, as well as the environments encountered in oil production regions. In the latter regard, the controllers are required to operate in environments ranging from desert to mountain to off-shore coastal facilities.
While electronic controller systems enjoy an expanded performance capability for improving production, electronic components and associated wiring are prone to attack by the corrosive environments within which they are called upon to operate. Solder and wiring are subjected to corrosion which, particularly in off-shore installations, is quite severe. Additionally, for the latter form of installation, the weather environments are severe to the extent that the controllers are subjected to submersion and high wind forces occasioned from hurricane conditions and the like. Thus, the controllers are subjected to weather and operationally induced dynamic forces as well as atmospheric environment attacks. Another aspect in providing adequate protection for the controllers resides in the simple failure of many operators to close up and seal containment boxes following their routine adjustment and inspection. In consequence, the controllers must be removed for factory servicing on a schedule which is undesirably accelerated.